/Engine/Plugins/Online/OnlineSubsystem/Source/Public/Interfaces/OnlinePartyInterface.h
Sends an invitation to a user that could not otherwise join a party if the player accepts the invite they will be sent the data needed to trigger a call to RequestReservation
true if task was started
bool SendInvitation ( const [FUniqueNetId](API\Runtime\CoreOnline\Online\FUniqueNetId) & LocalUserId, const [FOnlinePartyId](API\Plugins\OnlineSubsystem\FOnlinePartyId) & PartyId, const [FPartyInvitationRecipient](API\Plugins\OnlineSubsystem\Interfaces\FPartyInvitationRecipient) & Recipient, const [FOnSendPartyInvitationComplete](API\Plugins\OnlineSubsystem\Interfaces\FOnSendPartyInvitationComplete) & Delegate )